Thermoanalytical sensor, and method of producing the thermoanalytical sensor

ABSTRACT

In a thermoanalytical sensor with a substrate and a thermocouple arrangement that is formed at a measurement position on the substrate, an increase in sensitivity can be achieved by way of a special geometry of the thermocouple arrangement and/or the selection of the material for the substrate. In addition, a manufacturing method is proposed for the inventive sensor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to EuropeanApplication No. 03103996.9 filed in Europe on 28 Oct. 2003, the entirecontents of which are hereby incorporated by reference in theirentirety.

BACKGROUND

The invention relates to a thermoanalytical sensor with a substrate thatcan carry a heat flow between a heat source thermally coupled to thesubstrate and at least one measurement position formed on the sensor,and further with a thermocouple arrangement formed on a substantiallyplanar surface of the substrate to deliver a thermoelectric signal. Alsoincluded in the scope of the invention is a method of producing a sensorof this kind.

Thermoanalytical sensors of this kind are used to measure physicaland/or chemical properties of a substance, a substance mixture, and/or amixture undergoing a reaction, where the measurements are performed as afunction of temperature or time and where the sample that is beingmeasured is subjected to a controlled temperature program. Other knownexamples are the differential heat flow calorimetry and the differentialpower compensation calorimetry. In both of these applications, theanalysis of a sample is performed in relation to a reference sample. Thesensors being used in these cases therefore have two measurementpositions, i.e., one position to perform the measurements on the sampleand the other position to perform the measurements on the referencesample. In the first of the aforesaid applications, the thermoelectricsignal delivered by the thermocouple arrangement represents a measurefor the difference between the heat flow to the sample and the heat flowto the reference sample. In the second-named application, thethermoelectric signal delivered by the thermocouple arrangement is usedto control the respective heat flow rates to the sample and thereference sample in such a manner that the temperature differencebetween the sample and the reference sample is regulated to zero.

The thermoanalytical sensors can be configured to have the highestpossible degree of sensitivity covering, if possible, the entiretemperature range of the analysis, i.e., a thermoelectric signalproduced as a function of the heat flow is as strong as possible interms of signal voltage. This can help to obtain a good signal-to-noiseratio. Therefore, as a way to satisfy this, state-of-the-artthermoanalytical sensors (DE 39 16 311 C2 and EP 0 990 893 A1) have aseries of thermocouple junctions of the thermocouple arrangement joinedin a circuit in such a manner that the thermoelectric signal is producedas the sum of the individual thermocouple voltages. The thermocouplejunctions that form the thermocouple arrangement are laid out in acircular pattern around the center of the measurement position (oraround the centers of the measurement positions, if there is more thanone measurement position) spaced as closely as possible to each other inthe azimuthal direction. Consequently, there is no space available thatwould allow a further increase in the number of thermocouple junctionsin these state-of-the-art arrangements.

SUMMARY

Exemplary embodiments can solve the problem of achieving a furtherincrease in sensitivity in a thermoanalytical sensor.

Under a first exemplary aspect of the invention, a solution is proposedfor a thermoanalytical sensor with a substrate that can carry a heatflow between a heat source thermally coupled to the substrate and atleast one measurement position formed on the sensor, and further with athermocouple arrangement formed on a substantially planar surface of thesubstrate to deliver a thermoelectric signal, wherein the thermocouplearrangement includes a chain of thermocouple junctions which arecomposed of two different thermocouple materials and serially connectedto form a thermocouple column. The chain of thermocouple junctionsreaches in the azimuthal direction around the center of the measurementposition, with the individual thermocouple junctions arranged atalternatingly different radial distances from the center of themeasurement position. According to an exemplary embodiment, at least oneof the interstitial surface portions that are azimuthally confinedbetween a first thermocouple junction closest to the center and the twoimmediately neighboring second thermocouple junctions in the chaincontains a third thermocouple junction and a fourth thermocouplejunction that are direct neighbors to each other in the chain.

In the thermocouple column that is formed by this serially connectedchain of thermocouple junctions, any two thermocouple junctions that aredirect neighbors in the chain have a radial distance from each other.Thus, when there is a heat flow either in the direction towards thecenter of the measurement position or away from the center of themeasurement position, a temperature difference will occur between anytwo neighboring thermocouple junctions in the chain because of thethermal resistance of the sensor. The temperature difference, in turn,will give rise to thermo-voltages between neighboring thermocouplejunctions in the chain which, because of the serial chain arrangement,are added up as a voltage sum. Thus, the resultant overallthermoelectric signal represents the sum of the respective individualthermo-voltages that occur in each of the pairs of directly neighboringfirst and second thermocouple junctions as well as in the pairs ofdirectly neighboring third and fourth thermocouple junctions. The pairsof thermocouple materials can be the same for all of the thermocouplejunctions. One can also use a plurality of different pairs ofthermocouple materials to form the thermocouples instead of only onepair of different materials. As each of the pairs of directlyneighboring third and fourth thermocouple junctions is arranged in thefree interstitial space confined azimuthally between one of the firstthermocouple junctions and the two immediately neighboring secondthermocouple junctions, the space available on the sensor surface isoptimally utilized to increase the total number of thermocouplejunctions. In this arrangement, the third thermocouple junctions can bearranged at a relatively close radial distance to the first thermocouplejunctions, the latter being located at the shortest radial distance fromthe center of the measurement position, while the fourth thermocouplejunctions can be arranged at a relatively close radial distance to thesecond thermocouple junctions. A crucible that serves to hold ananalysis sample can be dimensioned so that in the measurement position,the bottom surface of the crucible covers the first and thirdthermocouple junctions, while the second and fourth thermocouplejunctions remain uncovered since they lie on a larger radius from thecenter of the measurement position. With a crucible designed in thismanner, the thermocouple arrangement can be particularly effective inmeasuring a radial temperature gradient that occurs in the vicinity ofthe crucible and corresponds to the heat flow exchanged between the heatsource and the crucible.

A particularly advantageous embodiment of the invention can use aconfiguration where the first thermocouple junctions lie on a firstcircle whose midpoint is located at the center of the measurementposition; the second thermocouple junctions lie on a second circleconcentric to and with a larger radius than the first circle; the thirdthermocouple junctions lie on a third circle concentric to the firstcircle and with a radius that is larger than the radius of the firstcircle but smaller than the radius of the second circle; and the fourththermocouple junctions lie on a fourth circle concentric to the firstcircle with a larger radius than the third circle. This arrangementconforms to the provision of radial symmetry of the measurement positionor positions (if the arrangement has more than one measurement position)relative to the center, and it also conforms to the customary radiallysymmetric shape of the sample crucibles that is compatible with thesymmetry requirement. The circular bottom surfaces of the cruciblesdesigned for use with this embodiment of the thermoanalytical sensor aredimensioned with a radius that is larger than the radius of the thirdcircle but smaller than the radius of the second circle.

To come as close as possible to a perfect radial symmetry, it is furtherhelpful that the thermocouples are arranged on their respective circlesat equal angular intervals. To make the radial symmetry as complete aspossible, it is likewise helpful that the thermocouple material betweenneighboring first and second thermocouple junctions in the chain extendsin the shape of rectilinear strip sections and that the thermocouplematerial between third and fourth thermocouple junctions that areimmediate neighbors in the chain and lie within the same interstitialarea likewise extends in the shape of rectilinear strip sections. Theoverall thermocouple arrangement in these cases has the appearance of adoubled-up star, i.e., two individual stars nested in each other andcentered on the midpoint of the measurement position. With this design,the surface area is used very efficiently, allowing the arrangement of aparticularly large number of thermocouple junctions and a commensuratelyhigh sensitivity of the sensor. As a further advantage, this arrangementis expandable by adding further nested stars as long as the insidecircle of thermocouple junctions of the outermost star has a smallerradius than the outside circle of thermocouple junctions of theinnermost star.

It further serves the purpose of achieving radial symmetry that thethermocouple material connecting each third thermocouple junction tothat of its neighboring fourth junctions which lies in the nextinterstice of the star contains an azimuthally directed track portion.This azimuthal track portion can take the shape of a segment of a circlewhose radius (from the midpoint of the measurement position) is slightlylarger than the circle radius of the second thermocouple junctions thatseparate the interstices of the star from each other. In thisarrangement, one end of the azimuthal portion can meet the end of atrack portion consisting of the other of the two thermocouple materialsto form the fourth thermocouple junction, while the other end of theazimuthal portion can continue into a radial portion extending to thethird thermocouple junction in the neighboring interstice.

To connect the thermoanalytical sensors to a processing circuit, it isof practical advantage that connector terminals are formed on thesurface of the substrate. These terminals are connected to the ends ofthe thermocouple column and serve to tap the thermoelectric sensorsignal. They can be configured in the shape of flat connector pads orconnector spots where connecting wires to a processing circuit can beattached.

In particular, it is envisaged within the scope of the invention thatmore than one of the measurement positions are arranged on the sensor.Specifically, one of the measurement positions can serve as referenceposition, while the other measurement positions serve to receive testsamples. The reference position can either remain empty, or it can beoccupied by an inert reference sample of known properties. If adifferential calorimetry experiment is to be performed, the respectivethermoelectric signals from the individual measurement positions can becombined through an appropriate circuit arrangement in such a mannerthat the respective differential signals between the reference positionand each of the sample positions can be obtained directly.

An exemplary embodiment of the inventive sensor has two measurementpositions arranged on one sensor unit. In this arrangement, one of themeasurement positions can be used as reference position and the other assample position. This configuration is analogous to arrangements usedfor differential heat flow calorimetry which will be familiar to thoseengaged in this field.

In an advantageous alternative embodiment of the invention, it isenvisaged to arrange four of the measurement positions on one sensorunit in a configuration where a straight line between the centers of onepair of the positions perpendicularly bisects a straight line betweenthe centers of the other pair, and vice versa. Thus, the centers of thefour measurement positions lie at the corners of an imaginary square.This arrangement is advantageous in that it optimizes the thermalsymmetry of all of the measurement positions.

The thermocouple arrangements in the sensors discussed up to this pointserve to sense a heat flow between the measurement position and the heatsource, or to sense a difference between heat flows associated withdifferent measurement positions. In addition, in thermoanalyticalapplications it is considered advantageous to provide embodiments of theinvention where a further thermocouple arrangement is formed at themeasurement position on the surface of the substrate for the purpose ofdelivering a thermoelectric signal representing the absolute temperatureat the measurement position, with separate connector terminals to tapthe signal representing the absolute temperature. It is a known factthat thermocouples can only provide a direct measurement of temperaturedifferences. If an absolute measurement is to be performed, thetemperature at one of the measurement positions has to be known or heldconstant. According to the state of the art, the exposure of one of themeasurement positions to the known temperature occurs outside of thesensor. The information that is thereby gained regarding the absolutetemperature of a measurement position can be used for example to performa mathematical correction of deviations from thermal symmetry in sensorswith a plurality of measurement positions in cases where such deviationsescape detection by a mere differential temperature measurement betweenthe measurement positions and where the failure to detect the deviationwould cause an error in the result of the analysis, because as aconsequence of the asymmetry, the temperature difference does notprecisely correlate to the difference between the heat flows at thedifferent measurement positions.

In a practical design configuration, the thermocouple arrangement thatserves to supply the thermoelectric signal representing the absolutetemperature has an area containing a first thermocouple material that isarranged in a surface portion delimited by the thermocouple junctionswhich surround the measurement position, with a connector portionleading to one of the connector terminals that are arranged on thesurface. In this configuration, the further thermocouple arrangement forthe sensing of the absolute temperature is concentrated around thecenter of the measurement position and thus in direct thermal contactwith the measurement position, i.e., with the sample that occupies themeasurement position. As a practical measure to optimize the radialsymmetry of the arrangement as much as possible, the delimited area ofthe first thermocouple material can, for example, be configured in theform of a circular ring.

In order to produce a thermoelectric signal representing the absolutetemperature and to make it possible to tap the signal, a thermocouplejunction with a second, different thermocouple material is arranged onthe delimited portion of the first thermocouple material, with thesecond thermocouple material extending to one of the connector terminalsformed on the surface.

An improvement in simplicity and a particularly efficient use of theavailable surface space on the sensor can be achieved through a designconfiguration where, for example, two of the measurement positions areformed on the sensor, with a connection between the second thermocouplematerials of the two measurement positions being formed on the substrateand routed to a common terminal. The thermoelectric signals representingthe absolute temperatures of the measurement positions are obtained bytapping the respective voltages between the common terminal and the twoterminals that are connected to the first thermocouple material at thetwo measurement positions.

In a further practical embodiment which has a purpose of, for example,minimizing the pattern of connector terminals that have to be arrangedon the substrate, two of the measurement positions are formed on thesensor and a connection is formed on the substrate between twoelectrically equivalent ends of the respective thermocouple columnsassociated with the measurement positions, while the other ends of thetwo thermocouple columns are connected to terminals that are formed onthe substrate and serve to tap the difference between the respectivethermoelectric signals of the two thermocouple columns. In thisconfiguration, the two thermocouple columns are connected so that theyoppose each other electrically, with the result that the thermoelectricsignal occurring at the two terminals represents a difference of thetemperatures at the two measurement positions.

For the evaluation of the results and the calculation of corrections, itcan further be desirable to provide a possibility for tapping therespective output signals of the two thermocouple columns separately.Again in the interest of minimizing the structure of connector terminalsrequired on the substrate, it is advantageous if the aforementionedconnection between the two electrically equivalent ends of thethermocouple columns is also connected to a common terminal formed onthe substrate. Thus, the respective output signal of each thermocouplecolumn can be tapped separately between the common terminal and theterminal at the other end of the respective thermocouple column.

Within the scope of the invention, it is envisaged in particular thatthe thermocouple arrangements formed on the substrate are configured asthick film arrangements. The concept of using thick film technology toproduce the thermocouple arrangements on the substrate is presented inthe above-referenced German patent DE 39 16 311 C2 and the underlyingGerman patent application publication DE 39 16 311 A1 with a discussionof the advantages that are achieved by using thick film technology. Thedisclosure of these two documents is hereby included by reference in thepresent disclosure. In particular, using thick film technology providesa simple solution to the problem of insulating the individual structuralelements of the thermocouple arrangements against the outside, i.e.,against sample crucibles or reference sample crucibles that are placedon the measurement positions.

To achieve the desired thermally inert behavior and durability of thesensor, it is advantageous if the substrate consists of or contains, aceramic material.

Under a second exemplary aspect of the invention, a further solution isproposed for a thermoanalytical sensor with a substrate that can carry aheat flow between a heat source thermally coupled to the substrate andat least one measurement position formed on the sensor, and further witha thermocouple arrangement formed on a substantially planar surface ofthe substrate to deliver a thermoelectric signal, wherein thethermocouple arrangement includes a chain of serially connectedthermocouple junctions which are composed of two different thermocouplematerials. According to an exemplary embodiment, the thermocouplejunctions are arranged in two or more planes that lie on top of eachother, with each plane being insulated from the next plane by aninsulating layer, each plane containing a section of the circuitarrangement, and each section being formed by conductor leads connectingthe thermocouple junctions, where the overall circuit arrangement isformed by connecting the appropriate ends of the sections to each otherby interlayer contacts.

According to the embodiment just outlined, the overall circuitarrangement is subdivided into at least two sections. As thethermocouple junctions that belong to the individual sections arearranged on top of each other, the available surface area on the sensoris multiplied in accordance with the number of planes that are layeredon top of each other. Consequently, the circuit arrangement can containa corresponding multiple of the number of thermocouple junctions. Theresult is a commensurate increase in the strength of the thermoelectricsignal delivered by the circuit arrangement and in the sensitivity ofthe sensor.

As an advantageous way of realizing the foregoing features, terminalsfor tapping the thermoelectric signal of the thermocouple arrangementare formed in the top plane relative to the substrate, and one end ofthe circuit section that occupies the bottom plane is connected to oneof the terminals through interlayer contact. The ability to tap thethermoelectric signal from the terminals lying in the top planefacilitates the installation and connection of the sensor in athermoanalytical instrument.

In an advantageous embodiment, the thermocouple junctions within asection of the circuit arrangement are connected in series and thesections, in turn, are serially connected to form the circuitarrangement, so that the result is a thermocouple column.

With preference, the thermocouple junctions are arranged so that theyproceed in the azimuthal direction around the center of the measurementposition and lie at alternatingly different radial distances from thecenter.

In a further advantageous configuration, the sections of the circuitarrangement that lie in different planes are of a substantiallycongruent shape.

Under a third exemplary aspect of the invention, a further exemplaryembodiment is proposed to provide in a thermoanalytical sensor with asubstrate that can carry a heat flow between a heat source thermallycoupled to the substrate and at least one measurement position formed onthe sensor, and further with a thermocouple arrangement formed on asubstantially planar surface of the substrate to deliver athermoelectric signal, wherein the thermocouple arrangement includes aserial chain of thermocouple junctions associated with the measurementposition, the junctions being composed of two different thermocouplematerials and connected into a circuit arrangement, and wherein thesubstrate has a thermal conductivity that does not exceed 5 Watt permeter and per degree Kelvin.

A thermal conductivity of this reduced magnitude in comparison to theconventional aluminum oxide substrates has the effect that a strongertemperature gradient develops between the thermocouple junctions thatare exposed to the different temperature levels. As a result, thethermoelectric signal produced by the thermocouple arrangement iscommensurately increased and, consequently, the sensitivity andsignal-to-noise ratio of the sensor are improved. However, as acautionary remark, as the thermal conductivity of the substrate isdecreased, the time constant of the sensor is increased. Even under thehypothetical assumption that materials technology imposes no limits onlowering the thermal conductivity, in an exemplary embodiment, a bottomlimit that should not be traversed is represented by a level of thermalconductivity where the time constant of the substrate is stillmarginally adequate.

In this regard, the range of interest for practical applicationsincludes materials with a thermal conductivity no lower than 0.5W/(m×K).

Using a low thermal conductivity, a conductivity value of, for example,no more than 3 W/(m×K) is preferred, with an even higher level ofpreference for values not exceeding 2 W/(m×K). This leads toparticularly noticeable improvements in comparison to conventionalaluminum oxide substrates.

In a practical embodiment, a special ceramic material is selected forthe substrate, with a lower conductivity value than the conventionalceramic oxide materials, but with favorable mechanical and electricalproperties comparable to the oxide ceramics. To name an example, thesubstrate material that is available under the trade name PYTHAGORAS hasbeen found suitable, having a thermal conductivity around 2 W/(m×K).Also suitable, albeit less desirable in regard to its mechanicalproperties, the glass ceramic substrate which is available under theproduct name MACOR has a thermal conductivity of significantly less than2 W/(m×K).

A fourth exemplary aspect of the invention relates to a method ofproducing a thermoanalytical sensor wherein a design pattern of at leasttwo different thermocouple material pastes is printed by way of athick-film technique onto a substantially planar surface of a substrate.The thick-film pattern, which is fired after printing, represents athermocouple arrangement with a serially connected chain of thermocouplejunctions composed of two different thermocouple materials andassociated with at least one measurement position, which serves todeliver a thermoelectric signal. An exemplary method is distinguished bythe fact that the circuit pattern is divided into at least two partialpatterns, that a first partial pattern is produced in thick-filmtechnology on the substrate, an insulating layer with contact passageholes for the connection of the partial patterns is overlaid on thefirst partial pattern, a further partial pattern is produced on theinsulating layer, and the foregoing procedure is repeated until allpartial patterns are produced above one another.

By using thick-film technology, the structure of the partial patternsand insulating layers can be produced on the substrate at a relativelylow cost. Conventional pastes can be used for the thermocouplematerials, for example gold paste for one of the thermocouple materialsand gold/palladium paste for the other thermocouple material. Ifdesired, it is possible to use other materials in order to producethermocouples with different properties. The pastes can be applied by aknown procedure using screen-printing techniques in accordance with theprescribed patterns. Each application of a pattern is followed by afiring operation. In particular, one can first apply and fire one of thethermocouple materials for each partial pattern and subsequently applyand fire the other thermocouple material in accordance with therespective partial pattern. Performing the two firing operationsseparately has a favorable effect on the thermoelectric conductivity ofthe thermocouples that are formed in the manner just described.

In advantageous embodiments of the inventive method, the partialpatterns are configured in such a way that the repetitive procedure ofapplying each partial pattern as a layer directly produces thethermoanalytical sensors with the preferred circuit configurations. In afirst embodiment of this kind, the partial patterns are designedsubstantially congruent to each other. In a further embodiment, eachpartial pattern is serially connected to the next by only oneconnection, whereby the number of interlayer connections can be keptsmall. In a further embodiment, the topmost partial pattern relative tothe substrate is overlaid with an insulating layer with connectorterminals from which the thermoelectric signal can be tapped, wherein atleast one of the connector terminals is joined through interlayercontact to the partial pattern in the bottom layer relative to thesubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

In the description that follows below, exemplary embodiments of theinvention are explained in more detail with references to the drawings,wherein:

FIG. 1 schematically represents a plan view of a thermoanalytical sensoraccording to a first exemplary embodiment of the invention arranged inthe area of a measurement position;

FIG. 2 schematically represents a plan view of a thermoanalytical sensoraccording to a second exemplary embodiment of the invention with twomeasurement positions;

FIG. 3 represents an exploded view of a thermoanalytical sensoraccording to a third exemplary embodiment of the invention;

FIG. 4 schematically represents a plan view of a thermoanalytical sensoraccording to a fourth exemplary embodiment of the invention; and

FIG. 5 represents an exploded view of a thermoanalytical sensoraccording to a fifth exemplary embodiment of the invention.

DETAILED DESCRIPTION

A thermoanalytical sensor according to a first exemplary embodiment ofthe invention has a cylindrical substrate 1, where the height of thecylinder is small in relation to its radius. FIG. 1 represents inschematic form a plan view of a top surface 2 of the substrate which hasthe shape of a circular disk, as seen in the direction of the cylinderaxis of the substrate 1. In the area delimited between the cylinder axisand the radially outer border of the surface 2, a measurement position 3is arranged which is equipped with a thermocouple arrangement that hasbeen put in place through a thick-film technology procedure.

In this thermocouple arrangement, strip-shaped sections of two differentthermocouple materials overlap at each of their adjoining ends, so thata series of thermocouple junctions is formed by these overlaps. Thethermocouple junctions are arranged on four concentric circles whosecommon center point 4 represents the center of the measurement position3. The first thermocouple junctions, which are located on the firstcircle closest to the center are identified in FIG. 1 by the referencesymbol 5. Each of the first thermocouple junctions is composed ofoverlapping, short azimuthal end portions of the two differentthermocouple materials 6 and 7. From the azimuthal end portions, thethermocouple materials 6 and 7 extend narrowly spaced from each otherand parallel to each other in a substantially outward radial directionrelative to the center 4 to a second circle, where the secondthermocouple junctions 8 are formed likewise by overlapping, shortazimuthal end portions analogous to the first thermocouple junctions 5.

The third thermocouple junctions 9 lie on the third circle, whose radiusis larger than the radius of the first circle and smaller than theradius of the second circle. Similar to the first thermocouple junctions5, the third thermocouple junctions 9 have short azimuthal overlappingend portions of the two thermocouple materials 6 and 7. From the thirdthermocouple junctions 9, the thermocouple materials 6 and 7 extendsubstantially in the shape of strip sections in an outward radialdirection to the fourth circle, whose radius is larger than the radiusof the second circle. The ends of the strips of the thermocouplematerial 7 lie on the fourth circle where they meet and overlap with theends of the thermocouple material 6 to form the fourth thermocouplejunctions 10. From the fourth thermocouple junctions 10, thethermocouple material 6 extends in the azimuthal direction following thefourth circle. Each of the azimuthal strip sections 11 of the firstthermocouple material 6 extends from a fourth thermocouple junction 10to the substantially radial strip section of the thermocouple material 6that originates from the azimuthally nearest neighboring thirdthermocouple junction 9. The first, second, third and fourththermocouple junctions 5, 8, 9, and 10, respectively, are arranged ontheir respective circles at equal azimuth-angle intervals from eachother.

Deviating from a completely symmetric configuration of the firstthermocouple junctions 5, one first thermocouple junction 5′ isdistinguished by the fact that the substantially radial strip section ofthe first thermocouple material 6′ which originates from the junction 5′continues beyond the radius of the second circle to a terminal pad 12that is formed on the surface 2 of the substrate 1. This firstthermocouple junction 5′ forms the end of a thermocouple column in whichall thermocouple junctions 5, 5′, 8, 9 and 10 are connected in a serialsequence. The other end of the thermocouple column is formed by thefourth thermocouple junction 10′ serially following the thirdthermocouple junction 9′ that lies radially next to the aforementionedfirst thermocouple junction 5′. The strip section of thermocouplematerial 7′ which runs from the third thermocouple junction 9′ in asubstantially outward radial direction is at its outer end on the fourthcircle joined to a strip section of the thermocouple material 6″ to formthe fourth thermocouple junction 10′. The strip section of thethermocouple material 6″ runs to a terminal pad 12′ that is formed onthe surface 2.

The drawing and the accompanying description given in the foregoingparagraphs also make it clear that the thermocouple materials 6, 7, 7′are, in an exemplary embodiment, overlaid on each other only in theareas where they mutually overlap and thereby, i.e., through the contactprovided by the overlap, form the thermocouple junctions 5, 5′, 8, 9,10, 10′. All other parts of the thermocouple materials 6, 7, 7′ runside-by-side in one and the same plane.

In the serially connected sequence that forms the thermocouple columnbeginning at the first thermocouple junction 5′, each first thermocouplejunction 5 or 5′ has a second thermocouple junction 8 as its immediateneighbor until the counterclockwise azimuthal loop about the centerpoint 4 has reached the first thermocouple junction 5″ which, in theazimuthal direction, lies next to the starting thermocouple junction 5′of the column. The junction 5″ is connected through the substantiallyradially directed strip section of the thermocouple material 7 to afurther thermocouple junction 8′ which has a third thermocouple junction9″ as its immediate neighbor in the serial sequence, followed by pairsof immediately neighboring fourth and third thermocouple junctions 10and 9, respectively, until the fourth thermocouple junction 10′ has beenreached which forms the other end of the thermocouple column. Theoverall thermocouple arrangement has the appearance of a doubled-upstar. The thermocouple materials 6, 7 that extend in the shape ofrectilinear strips between the first and second thermocouple junctions 5and 8 form an inner star and delimit between each other azimuthalinterstitial areas 13. In each of the interstitial areas 13 lies a pair9, 10 of third and fourth thermocouple junctions that are immediateneighbors in the serial sequence. The third and fourth thermocouplejunctions 9, 10 with their connecting strip sections of thermocouplematerials 6, 7 form the outer star. The arrangement could be continuedin analogous manner with a further azimuthal ambit in counterclockwisedirection starting at the thermocouple junction 10′.

A thermoelectric sensor according to a second exemplary embodiment ofthe invention is shown in FIG. 2, using an analogous form ofrepresentation as in FIG. 1. In this embodiment there are twomeasurement positions 3, 3′, each with a structure that is completelyequivalent to the measurement position 3 as described above in thecontext of FIG. 1. The reader is therefore referred to the descriptionof FIG. 1 for the structural details of the second embodiment. The twomeasurement positions 3 and 3′ of the second embodiment are arranged atequal distances diametrically opposite to each other relative to thecylinder axis of the substrate 1. The letter “S” for “Sample” is printedon the substrate surface 2 near the measurement position 3, and theletter “R” for “Reference” is printed near the measurement position 3′.This indicates that a sample is to be placed on the measurement position3, and an inert reference sample is to be placed on the measurementposition 3′.

The arrangement in FIG. 2 deviates from FIG. 1 only in that the fourththermocouple junction 10′ at the end of the thermocouple column formedat the measurement position 3 and likewise the fourth thermocouplejunction 10′ at the end of the thermocouple column formed at themeasurement position 3′ are not each connected to a separate terminalpad 12′ in analogy to the terminal pad 12′ in FIG. 1. Instead, theseends of the two thermocouple columns are joined by a strip section ofthe thermocouple material 6. The first thermocouple junctions 5′ thatform the other ends of the respective thermocouple columns at themeasurement positions 3 and 3′ are each connected to a terminal pad 12in the same manner as in FIG. 1. Through this design configuration, thetwo thermocouple columns are arranged so that they electrically opposeeach other in the circuit. Thus, by tapping the two terminal pads 12 inthe second embodiment, one obtains the difference between the respectivethermoelectric signals of the two thermocouple columns, while the firstembodiment delivers between the terminal pads 12, 12′ the entirethermoelectric signal produced by the thermocouple column that is formedon the measurement position 3.

In the thermoanalytical sensor according to a third exemplary embodimentof the invention, the overall pattern formed by the thermocouplematerials and thermocouple junctions of the thermocouple arrangement issubdivided into a plurality of partial patterns which are arranged ontop of each other, with the appropriate electrical terminations of thepartial patterns being connected to each other. This concept isillustrated in FIG. 3, shown in an exploded view for the sake ofclarity, wherein the individual strata of the layered arrangement areshown pulled apart from each other in the direction of the cylinder axisof the substrate 1 which is identical to the substrates shown in FIGS. 1and 2. The arrangement of FIG. 3 has a total of three partial patterns14, 15 and 16, respectively, each of which is configured analogously tothe pattern forming the thermocouple arrangement in the secondembodiment which is represented in FIG. 2. Minor deviations from thepattern shown in FIG. 2 exist only to the extent necessary for formingthe connections of the electrical terminations of the partial patterns.

In FIG. 3, the partial pattern 14 at the bottom is arranged on thesurface 2 of the substrate in the same manner as in FIG. 2. Likewise asin FIG. 2, the thermocouple material from the first thermocouplejunction 5′ that forms one end of the overall circuit arrangementrepresented by the entire pattern is connected to the terminal pad 12.Also as in FIG. 2, the part of the pattern shown on the left side isjoined to the right-hand part by means of the connecting strip 6 ofthermocouple material. However, in contrast to FIG. 2, the analogousfirst thermocouple junction at the end of the right-hand part in FIG. 3is connected to an interlayer contact pad 17 which is arranged at adistance from the left-hand terminal pad 12 in FIGS. 2 and 3 as well asfrom a second terminal pad 12 that corresponds to the right-handterminal pad in FIG. 2 but is configured as an insular pad in FIG. 3,i.e., non-contiguous with the rest of the partial pattern.

The partial pattern 14 that is arranged on the surface 2 is topped by aninsulating layer 18 that is equipped with interlayer contact holes 19 atmatching positions for the interlayer contact pad 17 and the twoterminal pads 12. On the surface 20 that faces away from the partialpattern 14, the insulating layer 18 carries the partial pattern 15. Atthe analogous position where the bottom-layer partial pattern 14 has anend connection to the terminal pad 12, the middle-layer partial pattern15 has an end connection to an interlayer contact pad 17′ which isconnected to the interlayer contact pad 17 by way of the interlayercontact hole 19 that is congruent with the interlayer contact pads 17and 17′. Where the bottom-layer partial pattern 14 has an end connectionto the interlayer contact pad 17, the right-hand part of the partialpattern 15 in FIG. 3 has an analogous end connection to an interlayercontact pad 21 which is electrically insulated against the bottom layerby the insulating layer 18. The two terminal pads 12 of the bottom layerare brought out through the congruently positioned interlayer contactholes 19 to the surface 20 of the insulating layer 18 where they appearas insular pads.

The surface 20 of the insulating layer 18 which carries the partialpattern 15 is topped by an insulating layer 22 that is equipped withinterlayer contact holes 19′ at matching positions for the interlayercontact pad 21 and the two terminal pads 12. The surface 23 of theinsulating layer 22 carries the partial pattern 16, which forms thetopmost partial pattern in FIG. 3. The end connection of the left-handpart leads to an interlayer contact pad 17″ which is connected to thecongruently positioned interlayer contact pad 17′ of the middle-layerpartial pattern 15 by way of a likewise congruently positionedinterlayer contact hole 19′ of the insulating layer 22. The endconnection of the right-hand part leads to the right-hand terminal pad12 in FIG. 3, which is contacted directly through all layers by way ofcongruently located interlayer contact holes 19′ and 19 of theinsulating layers 22 and 18, respectively. The left-hand terminal pad 12connects through analogous interlayer contact holes 19′ and 19 to theleft-hand terminal pad 12 of the bottom-layer partial pattern 14 in FIG.3.

On top of the surface 23 of the insulating layer 22 that carries thetopmost partial pattern 16 there is an insulating layer 24 equipped onlywith interlayer contact holes 19″ that match the positions of theterminal pads 12. The thermoelectric signal delivered by the entirecircuit arrangement can be tapped at the terminal pads 12 that arecontacted through the interlayer contact holes 19″. The signalrepresents the sum of the thermo-voltage differences delivered by theindividual partial patterns 14, 15 and 16 between the left-hand part andthe right-hand part of each partial pattern.

Furthermore, in addition to the symbols “R” and “S” mentioned already inthe context of FIG. 2, the exposed surface 25 of the insulating layer 24carries arc-shaped markings 26 to facilitate the centered positioning ofthe sample- and reference crucibles relative to the center points 4 and4′ of the respective measurement positions (see FIG. 2).

The third embodiment shown in FIG. 3 can be produced in particular withthe use of thick-film technology. The process starts by screen-printingand firing the partial pattern 14 with suitable thermocouple materialpastes on the surface 2 of the substrate 1. This operation preferablycan be performed in two steps, the first of which consists of theapplication and immediate firing of only those structural components ofthe pattern that consist of a first thermocouple material. In the secondstep, the structural elements consisting of the other thermocouplematerial are printed and the firing is repeated. This two-step procedurehas a favorable effect on the quality of the thermocouple junctions.After the insulating layer 18 has been put in place, the second partialpattern 15 is produced in the same manner, and the foregoing procedureis repeated until all insulating layers and partial patterns have beencompleted, at which point the topmost insulating layer 24 is put inplace.

The thermoanalytical sensor according to a fourth exemplary embodimentof the invention is shown in FIG. 4 in a form of representation that isanalogous to FIG. 1. This fourth embodiment has a total of fourmeasurement positions 30, 31, 32 and 33, respectively, each of which hasan analogous configuration to the measurement position 3 in FIG. 1. Inregard to the individual measurement position, the reader is thereforereferred to the description of the embodiment shown in FIG. 1.Particularly like in FIG. 1, the end portions of the individualthermocouple columns are connected to a pair of terminal pads 12, 12′where the thermoelectric voltage can be tapped that is produced by therespective column. The centers of the four measurement positions 30, 31,32, 33 are located on the corners of a square whose diagonals intersectin the cylinder axis of the substrate 1.

The thermoanalytical sensor according to a fifth embodiment of theinvention is shown in FIG. 5 in an exploded view where the layers of thearrangement are pulled apart in the direction of the cylinder axis ofthe substrate 1. In regard to the differential circuit arrangement thatis formed between the two doubled-up star patterns by means of theconnector 6 and the two terminal pads 12, the fifth embodiment iscompletely analogous to the second embodiment which is described in thecontext of FIG. 2. Insofar as the differential circuit arrangement isconcerned, the reader is therefore referred to the description of FIG.2. However, FIG. 5 additionally shows an insulating layer 34 which isalso present in the second embodiment but is not shown in FIG. 2. Theinsulating layer 34 has windows 35 matching the locations of theterminal pads 12 of the thermocouple arrangement, so that thedifferential thermoelectric signal can be accessed at the windows 35.The insulating layer 34 allows metallic crucibles to be placed on themeasuring positions without thereby causing short circuits between thethermocouple junctions.

In addition to the features which have just been described and arealready part of the second embodiment in accordance with FIG. 2, thefifth embodiment has at each of the two measurement positions 3, 3′ afurther thermocouple arrangement 36, 36′, respectively, on the exposedsurface 37 of the insulating layer 34. Each of these furtherthermocouple arrangements 36, 36′ includes a ring-shaped firstthermocouple material 38, 38′ in a centered arrangement relative to thecenter 4, 4′ of the respective measurement position 3, 3′. In FIG. 5,the two further thermocouple arrangements 36, 36′ are, for the sake ofclarity, drawn to a magnified scale in comparison to the lower parts ofthe exploded drawing. In actuality, the ring-shaped first thermocouplematerial 38, 38′ is arranged within the respective first circle on whichthe first thermocouple junctions 5 are located. In the areas delimited,respectively, by the inside perimeters 39, 39′ of the ring-shapedarrangements 38, 38′, the insulating layer 34 and the substrate eachhave respective congruently located axial passage openings 40, 40′ and41, 41′. Passage openings of this kind also exist in the other,previously described embodiments and are identified with correspondingreference symbols in the respective drawing figures.

Each of the ring-shaped first thermocouple materials 38, 38′ has astrip-shaped radial extension leading, respectively, to the terminalpads 43, 43′. Furthermore, there is a common terminal pad 44 arranged onthe centerline that runs perpendicular to an imaginary connecting linebetween the respective center points 4, 4′ of the measurement positions3, 3′. Originating from the common terminal pad 44, a connecting lead 45runs along the centerline between the two terminal pads 43, 43′ to aY-shaped juncture where the connecting lead 45 branches out into twostrip-shaped arms 46, 46′ which extend in mirror-symmetry relative tothe centerline into the ring-shaped first thermocouple materials 38 and38′, respectively. The terminal pad 44, the connecting lead 45 and itsarms 46, 46′ consist of a second thermocouple material which formsthermocouple junctions at the connections to the first thermocouplematerials 38 and 38′. The thermoelectric signals that occur at these twothermocouple junctions can be tapped between the common terminal pad 44and the respective terminal pads 43 and 43′. The two thermoelectricsignals correspond to the respective absolute temperatures at themeasurement positions 3 and 3′. For the determination of the absolutetemperature values, the signal is further processed in a known mannerthrough an appropriate circuit arrangement.

In all embodiments of the foregoing description, the sensor is thermallycoupled to a heat source through thermal contact between a border areaof the substrate 1 and the heat source. This can be achieved, e.g., if aring-shaped border area of the bottom side of the sensor, i.e., thereverse side of the top surface 2, is seated on an appropriately shapedheat-conducting flange of the heat source. Specifically, the ring-shapedborder area can be delimited on the outside by the radially outer borderof the cylindrical disk that forms the substrate 1 and on the inside bya cutback in the shape of a flat cylinder whose radius is somewhatsmaller than the radius of the substrate 1.

The radial temperature gradients that occur relative to the centerpoints 4, 4′ of the measurement positions 3, 3′, 30, 31, 32, 33 are thereason for the thermoelectric voltages that are generated between thethermocouple junctions 5 and 8 as well as between the junctions 9 and10, which are radially distanced from each other. These temperaturegradients increase with decreasing thermal conductivity of the substrate1. Therefore, in order to achieve a high sensitivity of the sensor,substrates with a relatively small thermal conductivity λ can be used,specifically with λ not exceeding 5 W/(m·K), preferably with λ notexceeding 3 W/(m·K) or even not exceeding 2 W/(m·K). Substrates 1 thathave been found suitable are ceramics with special properties, forexample made of the ceramic material that is available under the tradename PYTHAGORAS, or made of the glass-ceramic material that is availableunder the trade name MACOR, which has a λ-value of about 1.5 W/(m·K).

It will be appreciated by those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof. The presently disclosedembodiments are therefore considered in all respects to be illustrativeand not restricted. The scope of the invention is indicated by theappended claims rather than the foregoing description and all changesthat come within the meaning and range and equivalence thereof areintended to be embraced therein.

1. A thermoanalytical sensor comprising: a substrate that can conduct aheat flow between a heat source that is thermally coupled to thesubstrate and at least one measurement position that is formed on thesensor; and a thermocouple arrangement formed on a substantially planarsurface of the substrate to deliver a thermoelectric signal, wherein thethermocouple arrangement comprises: a serial chain of thermocouplejunctions that are composed of two different thermocouple materialsserially connected to form a thermocouple column, wherein the serialchain of thermocouple junctions extends in an azimuthal direction arounda center of the measurement position; at least one interstitial area ofthe surface is azimuthally confined between a first thermocouplejunction closest to the center and two immediately neighboring secondthermocouple junctions in the serial chain; wherein the chain comprisesa first thermocouple junction connected to a second thermocouplejunction of the chain, and a third thermocouple junction connected to afourth thermocouple junction of the chain, such that the first, second,third, and fourth thermocouple junctions are arranged at differentradial distances from the center of the measurement position.
 2. Athermoanalytical sensor according to claim 1, wherein thermocouplematerial between the first and second thermocouple junctions in theserial chain extends in a shape of rectilinear strip-sections.
 3. Athermoanalytical sensor according to claim 1, wherein thermocouplematerial between the third and fourth thermocouple junctions that areimmediate neighbors in the serial chain and lie within the sameinterstitial area extends in a shape of rectilinear strip sections.
 4. Athermoanalytical sensor according to claim 1, wherein the thermocouplematerial runs from the fourth thermocouple junctions of the chain to thethird thermocouple junctions of the chain, and includesazimuthally-directed strip sections.
 5. A thermoanalytical sensoraccording to claim 1, wherein connector terminals are formed on thesurface of the substrate, said connector terminals being respectivelyconnected to two ends of the thermocouple column, wherein thethermoelectric signal delivered by the thermocouple column can be tappedfrom said connector terminals.
 6. A thermoanalytical sensor according toclaim 1, wherein the substrate is a ceramic material.
 7. Athermoanalytical sensor according to claim 1, wherein the firstthermocouple junction lies on a first circle whose midpoint is locatedat the center of the measurement position, the second thermocouplejunctions lie on a second circle concentric to and with a larger radiusthan the first circle, the third thermocouple junction lies on a thirdcircle that is concentric to the first circle and has a radius that islarger than the radius of the first circle and smaller than the radiusof the second circle, and the fourth thermocouple junction lies on afourth circle that is concentric to the first circle and has a largerradius than the second circle.
 8. A thermoanalytical sensor according toclaim 7, wherein the thermocouple junctions of a chain are arranged ontheir respective circles at equal angular intervals.
 9. Athermoanalytical sensor according to claim 1, wherein a plurality of themeasurement positions are arranged on the sensor.
 10. A thermoanalyticalsensor according to claim 9, wherein two of the measurement positionsare arranged on the sensor.
 11. A thermoanalytical sensor according toclaim 9, wherein four measurement positions are arranged on the sensorin a configuration where a straight connecting line between centers ofone pair of the measurement positions perpendicularly bisects a straightline between the centers of the other pair, and vice versa.
 12. Athermoanalytical sensor according to claim 1, wherein the substrate is aceramic substrate whose thermal conductivity is not larger than 5 Wattper meter and Kelvin.
 13. A thermoanalytical sensor according to claim12, wherein the substrate comprises a glass-ceramic material.
 14. Athermoanalytical sensor according to claim 12, wherein the substrate isa ceramic substrate whose thermal conductivity is not larger than 3 Wattper meter and Kelvin.
 15. A thermoanalytical sensor according to claim12, wherein the substrate is a ceramic substrate whose thermalconductivity is not larger than 2 Watt per meter and Kelvin.
 16. Athermoanalytical sensor according to claim 1, wherein a furtherthermocouple arrangement is formed at the measurement position on thesurface of the substrate for delivering a thermoelectric signalrepresenting absolute temperature at the measurement position, andconnector terminals for tapping the thermoelectric signal representingthe absolute temperature are formed on the surface of the substrate. 17.A thermoanalytical sensor according to claim 16, wherein thethermocouple arrangement that serves to deliver the thermoelectricsignal representing the absolute temperature comprises an areacontaining a first thermocouple material, said area being delimited bythe thermocouple junctions which surround the measurement position, andfurther comprises a connector portion leading from said delimited areacontaining the first thermocouple material to one of the connectorterminals that are arranged on the surface.
 18. A thermoanalyticalsensor according to claim 17, wherein said delimited area containing thefirst thermocouple material is configured in a shape of a circular ring.19. A thermoanalytical sensor according to claim 18, wherein in thedelimited area containing the first thermocouple material, athermocouple junction is formed with a second thermocouple material thatis different from the first thermocouple material and extends to aconnector terminal that is formed on the surface.
 20. A thermoanalyticalsensor according to claim 19, wherein two measurement positions areformed on the sensor, a connection is formed on the substrate betweenthe second thermocouple materials of the two measurement positions, andsaid connection leads to a common connector terminal.
 21. Athermoanalytical sensor according to claim 19, wherein thermocouplearrangements that are formed on the substrate are configured as thickfilm arrangements.
 22. A thermoanalytical sensor according to claim 19,wherein two measurement positions are formed on the sensor, a connectionis formed on the substrate between two electrically equivalent ends ofrespective thermocouple columns at the measurement positions, and otherends of the two thermocouple columns are connected to connectorterminals that are formed on the substrate and serve to tap a differencebetween respective thermoelectric signals of the two thermocouplecolumns.
 23. A thermoanalytical sensor according to claim 22, whereinthe connection is connected to a common connector terminal that isformed on the substrate.